In typical commercial reproduction apparatus (electrostatographic copier/duplicators, printers, or the like), a latent image charge pattern is formed on a uniformly charged dielectric member. Pigmented marking particles are attracted to the latent image charge pattern to develop such image on the dielectric member. A receiver member is then brought into contact with the dielectric member. An electric field, such as provided by a corona charger or an electrically biased roller, is applied to transfer the marking particle developed image to the receiver member from the dielectric member. After transfer, the receiver member bearing the transferred image is separated from the dielectric member and transported away from the dielectric member to a fuser apparatus at a downstream location. There the image is fixed to the receiver member by heat and/or pressure from the fuser apparatus to form a permanent reproduction thereon.
One type of fuser apparatus, utilized in typical reproduction apparatus, includes at least one heated roller and at least one pressure roller in nip relation with the heated roller. The fuser apparatus rollers are rotated to transport a receiver member, bearing a marking particle image, through the nip between the rollers. The pigmented marking particles of the transferred image on the surface of the receiver member soften and become tacky in the heat. Under the pressure, the softened tacky marking particles attach to each other and are partially imbibed into the interstices of the fibers at the surface of the receiver member. Accordingly, upon cooling, the marking particle image is permanently fixed to the receiver member.
It has been found that the gloss (finished luster) of a fused image is, at least in significant part, due to the temperature at which fusing is accomplished. Further, image gloss needs to be substantially uniform across any individual receiver member, as well as from receiver member to receiver member during a reproduction apparatus job run, to yield high quality reproductions consistent over the job runs. However, as soon as a receiver member passes through the fuser roller nip, the temperature at the outer surface of the fuser roller droops very quickly. Since the temperature droops from the operating setpoint, the logic and control for the reproduction apparatus turns on the fuser heating device. Then, depending upon the thickness of the fuser roller, there is a time lag until the fuser roller surface receives enough energy to get back to the desired fusing temperature setpoint. Therefore, during the time lag, the droop in surface temperature causes inferior fusing quality. When the reproduction apparatus is a process color machine, the temperature droop results in objectionable lower saturation of colors and image gloss. When the receiver member is of a dimension in the direction of travel which requires the fusing roller to rotate through greater than 360.degree. to accomplish fusing, the fusing roller cannot recover to the temperature setpoint. As a result the image will be fused at two distinct fuser temperatures and exhibit two distinct gloss regions. This condition is, of course, objectionable and usually unsatisfactory to the customer.